Bottom Line:
However, the specific and causal contributions of different brain regions in this pathway, including the middle-lateral (ML) and anterolateral (AL) belt regions of the auditory cortex, to auditory decisions have not been fully identified.Both ML and AL neural activity was modulated by the frequency content of the stimulus.Together, these findings suggest that AL directly and causally contributes sensory evidence to form this auditory decision.

Affiliation: Department of Otorhinolaryngology, University of Pennsylvania, Philadelphia, Pennsylvania, USA.

ABSTRACTAuditory perceptual decisions are thought to be mediated by the ventral auditory pathway. However, the specific and causal contributions of different brain regions in this pathway, including the middle-lateral (ML) and anterolateral (AL) belt regions of the auditory cortex, to auditory decisions have not been fully identified. To identify these contributions, we recorded from and microstimulated ML and AL sites while monkeys decided whether an auditory stimulus contained more low-frequency or high-frequency tone bursts. Both ML and AL neural activity was modulated by the frequency content of the stimulus. But, only the responses of the most stimulus-sensitive AL neurons were systematically modulated by the monkeys' choices. Consistent with this observation, microstimulation of AL, but not ML, systematically biased the monkeys' behavior toward the choice associated with the preferred frequency of the stimulated site. Together, these findings suggest that AL directly and causally contributes sensory evidence to form this auditory decision.

Figure 4: Neuronal sensitivity to stimulus frequency and coherence in ML (top) and AL (bottom)a, Single-neuron examples of responses from correct trials. Color corresponds to stimulus coherence. Grey lines show low-coherence responses separated by choice, as indicated. Left panels show activity aligned to stimulus onset. Right panels show activity aligned to the onset of joystick movement. b, Population histograms from correct trials, plotted as in a except that coherence is encoded with respect to each neuron’s preferred and non-preferred frequency (see legend).

Mentions:
Both ML and AL auditory-driven responses were modulated by the frequency content of the stimulus. For the example ML neuron shown in Fig. 4a, top, the preferred frequency was assigned to the high-frequency value of the tone-burst sequence. Consequently, as signed coherence approached +100%, the firing rate of the neuron increased. This coherence-dependent modulation had a strong phasic increase in activity that started <~50 ms after stimulus onset and then persisted for a few hundred ms. For the example AL neuron shown in Fig. 4a, bottom, because the preferred frequency was assigned to the low-frequency value, its firing rate increased as signed coherence approached −100%. The response of this neuron, like the ML neuron, had coherence-dependent modulations but had slightly later response onsets and more sustained, coherence-dependent responses throughout stimulus presentation. At the population level, both ML and AL showed qualitatively similar trends as these two example units, in both cases showing sensitivity to signed coherence that for ML was most prominent just after stimulus onset but for AL was more persistent throughout stimulus presentation (Fig. 4b).

Figure 4: Neuronal sensitivity to stimulus frequency and coherence in ML (top) and AL (bottom)a, Single-neuron examples of responses from correct trials. Color corresponds to stimulus coherence. Grey lines show low-coherence responses separated by choice, as indicated. Left panels show activity aligned to stimulus onset. Right panels show activity aligned to the onset of joystick movement. b, Population histograms from correct trials, plotted as in a except that coherence is encoded with respect to each neuron’s preferred and non-preferred frequency (see legend).

Mentions:
Both ML and AL auditory-driven responses were modulated by the frequency content of the stimulus. For the example ML neuron shown in Fig. 4a, top, the preferred frequency was assigned to the high-frequency value of the tone-burst sequence. Consequently, as signed coherence approached +100%, the firing rate of the neuron increased. This coherence-dependent modulation had a strong phasic increase in activity that started <~50 ms after stimulus onset and then persisted for a few hundred ms. For the example AL neuron shown in Fig. 4a, bottom, because the preferred frequency was assigned to the low-frequency value, its firing rate increased as signed coherence approached −100%. The response of this neuron, like the ML neuron, had coherence-dependent modulations but had slightly later response onsets and more sustained, coherence-dependent responses throughout stimulus presentation. At the population level, both ML and AL showed qualitatively similar trends as these two example units, in both cases showing sensitivity to signed coherence that for ML was most prominent just after stimulus onset but for AL was more persistent throughout stimulus presentation (Fig. 4b).

Bottom Line:
However, the specific and causal contributions of different brain regions in this pathway, including the middle-lateral (ML) and anterolateral (AL) belt regions of the auditory cortex, to auditory decisions have not been fully identified.Both ML and AL neural activity was modulated by the frequency content of the stimulus.Together, these findings suggest that AL directly and causally contributes sensory evidence to form this auditory decision.

Affiliation:
Department of Otorhinolaryngology, University of Pennsylvania, Philadelphia, Pennsylvania, USA.

ABSTRACTAuditory perceptual decisions are thought to be mediated by the ventral auditory pathway. However, the specific and causal contributions of different brain regions in this pathway, including the middle-lateral (ML) and anterolateral (AL) belt regions of the auditory cortex, to auditory decisions have not been fully identified. To identify these contributions, we recorded from and microstimulated ML and AL sites while monkeys decided whether an auditory stimulus contained more low-frequency or high-frequency tone bursts. Both ML and AL neural activity was modulated by the frequency content of the stimulus. But, only the responses of the most stimulus-sensitive AL neurons were systematically modulated by the monkeys' choices. Consistent with this observation, microstimulation of AL, but not ML, systematically biased the monkeys' behavior toward the choice associated with the preferred frequency of the stimulated site. Together, these findings suggest that AL directly and causally contributes sensory evidence to form this auditory decision.